Dynamo-electric machine



Dec 17, 1929- N. oBouKHoFF ADYNAMO ELECTRIC MACHINE Filed Dec. 5, 1923 2 Sheets-Sheet 1 Snor um* N. OBCUKHOFF DYNAMO ELECTRIC MACHINE Dec; 17, 1929,

Filed Dec. 5, 1925 i i A Patented Dec. 17, 1929 nire STATES PATENT orrice NIKOLAI OBOUKHOFF, F BARBIN, CH'INA DYNAMO-ELECTRIC MACHINE Application filed December ,5, 19,23, Serial N o, 678,532, and ,in `France March 14, 1923.

This invention relates to certain improvements in dynamo electric machines for generating electro-motive forces of relatively high frequencies, and is intended primarily as an improvement upon my earlier invention, disclosed in U. S. Letters Patent granted to me, No, 1,426,001, dated August 15, 192,2. In its broader aspects, however, the present invention is not intended to be limit- 19 ed in its application to machines of the type shown in the patent referred to; but is capa? ble of use generally with other types of alternating current generators where it is desirable to supply or generate current of high frequency of alternation by means of a dynamo electric machine.

In order to increase the frequency of the E. Mv. F. of a given dynamo electric machine, it is usually necessary to increase the peripheral speed of the rotating element (rotor); and in obtaining the relatively high 'frequencies with the usual or commercial alternator, practical difficulties are encountered at the higher speeds due in large part to the increase in iron losses and heating ofthe machine, It is possible to attain equally high frequencies, without materially increasing the speed of rotation of the revolving element (rotor), by reducing the pitch of the teeth of both rotor and stator (the tooth pitch for bothelements being the same); but this expedient gives only unsatisfactory results in practice, in that it tends to reduce the available space between successive teeth of the element, either rotor or stator, to receive the windings and their insulation, while the excessive iron and heat losses remain the same or are increased in relation to the power of the dynamo. For generating` high frequency currents of any appreciable voltage and .amperage I have found either of these methodsto be of limited practical value. The controlling factors to be considered, therefore, in designing a high frequency alternator are the excessive iron losses, and undue heating o f the machine. I have discovered principles of design and the construction o f a machine by which the above mentioned losses are minimized, and with which at peripheral speeds which are not excessive, it is possible to generate alternating ,currents of relatively high frequency, in an ,efficient Iand practical Way. The first part of my invention relates to means for yielding or generating the increased frequencies without unduly increasing the speed of rotation of the revolving element, and maintaining the iron losses within practical limits while at the same time affording ample space ,for the windings of the element which is to be wound either stator or rotor and thus securing appreciable voltage, amperage and power; and the second part A0f my invention relates to the physical construction of the component elements of the machine to promote the circulation of cooling currents of air whereby the excessive heating of the machine is substantially reduced.

My inventiOIl is hereinafter explained in detail in `connection with the accompanying drawings which form a part of disclosure .and are illustrative of the invention. The principles of the invention, however, are capable of application to other types of machines than those shown in the drawings, and the invention is not to 'belimited by the illustrative showing. In these drawings, in which the same reference characters are used to indicate corresponding parts in each of the figures:

Figs. 1 and 2 iare sectional developments ofthe rotor and stator elements of an alternator showing a selected relation of tooth pitches and Islot widthson the two elements.

n Fig. 2 the windings of the stator are omitted and the rotor has been displaced by an angle corresponding to a peripheral disstane equal to one-half of the `width of a rotor tooth or one-fourthof the pitch of Kthe rotor teeth.

Figs. 3 and 4 are similar views of a modi-` 90 fied or different relation between pitch of stator tooth to that of the rotor; and like the arrangement of Figs. 1 and 2 is intended to generate high frequency currents with minimized iron losses, and also to afford ample width of slot for the windings.

Figs. 5 and `5a are views showing further sectional developments of modified and selected relations between the pitch of tooth crowns on the rotor and stator elements, as

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`both ot' these views the pitch of the stator and rotor teeth is the same, but the width of the stator slots, bears a dilerent ratio in each case to the width of the rotor slots.

Fig. G is the curve of E. M. F. generated in the winding of the machine of Fig. 5.

Fig. 6b is the curve of E. M. F. generated in winding ot the machine of Fig. 7, dilering from that ot Fig. 6, in that the intervals ot Zero voltage-value are relatively large.

Figs. 7 and 7a are views of sectional developments of further moditications ot selected relationships between the pitch and width of slots ot rotor and stator elements.

Fig. 8 is a sectional elevation of a special type oit' dynamo electric machine embodying the principles ot' my invention, the stator element being designed with a view to reducing or minimizing the iron losses and concentrating the excitation or magnetizing winding in a relatively small number ot slots so as to use the whole space of peripherally distributed slots for the alternating current windings.

Fig. 9 is a sectional development ot a machine similar to that ot Fig. 1 with the stator teeth arranged at an angle to the diametrical planes passing through the teeth.

Referring now to Figs. 1 and 2, St is the wound stator element with tooth projections DS; and Rt is the rotor provided with a toothed crown, the teeth ot' which are indicated at 1),.. The stator windings comprise a magnetizing or field winding O, and primary and secondary windings 1 and 2. The magnetizing winding O, is so arranged that any two adjacent teeth will have opposite polarity indicated by the letters N and S in Fig. 2. rlChe stator slots are lettered ES and those oit the rotor E...

The pitch of the stator teeth, as shown in these figures is 1.5 times that ot the rotor teeth, and the width of the stator slots is twice that ot the rotor slots. The width oi the stator tooth is equal to the width of the rotor tooth. In the relative position of stator and rotor teeth shown in Fig. 1. the conductance ot the magnetic circuit, (circuit shown in dotted lines) is a minimum, while in Fig. 2, where relative positions of the elements has been changed by a displacement of the rotor periphery equal to one-half the width ot a rotor tooth, the magnetic conductance is at its maximum value. A com plete cycle of magnetic change in this machine will theretore be effected by moving of the rotor element through an angle corresponding to a peripheral displacement of ene-hall` ot the rotor pitch or gb lt would be the same if the width of a stator tooth or oi' a rotor tooth or of both were less and the width of a stator slot or of a rotor slot or ot both were greater than is given in Figures l and 2, provided the pitch of the stator teeth be 1.5 times that ot the rotor teeth.

It the tooth pitch of the rotor and stator were equal, it is obvious that the movable element must be displaced by a distance equal to the tooth pitch in order to complete a cycle et magnetic change; and since this change is accomplished in the machine oi' Fig. l, by one-half such angular displacement oit the rotating part, it -follows that at the same angular velocity, it will generate on E. M. F. having double the 'frequency et that produced where the pitch ot rotor and stator teeth is the same. Since this result is obtained by increasing the pitch of the teeth ot one element (instead ot the usual method of decreasing the tooth pitch of both elements) there is a lesser total ot' tooth projections, and a corresponding reduction in the iron losses. At the same time the width oit slot of the stator element is increased, allowing for enlarged crosssection ol' active conductors and also better or improved insulation, as well as reducing magnetic leakage iiuxes across slots and consequently the value of the magnetic induction in teeth, iron losses and heating therein being accordingly diminished. The total section ot all the stator slots in this machine is fi/ times as large as in the case where the tooth pitches ot rotor and stator are equal; and consequently there is a gain ot' Sill/3% in the space available for receiving the windings. lt will be apparent, therefore, that it is entirely practical to use rotor pitches, which are very much smaller than are recognized as the limitingcase where the stator pitch is the same as the rotor pitch and the stator slots are too limited in width as to properly accomi'nodate the required windings with their insulation. It will also be apparent that the rotor element may be the wound element, and in this case the relationship ot tooth pitches and width ot slots would be reversed in order, so that the rotor -tooth pitch would be 1.5 times that of the stator. In general modilications oit this machine are permissible in accordance with the expression.

Stator pitch 222i rotor pitch Ps P,

where n may be any whole number including Zero (l, 2, 3 etc.) In every instance where the above expressed relationship is maintained the frequency oi the generated E. M. F. will be twice that obtainable with the same angular speed where the tooth pitch ot the two elements is the same.

Figs. 3 and 4L illustrate another selected relationship between the pitches ot stator and rotor elements ot an alternator, the details of which are designated by the same reference led ACn

characters as in Figs. 1 andQ. Here ,the pitch of the stator gteeth has been selected to be twice that .of lthe rotor. Also the arrange.- ment is such that the stator slot ES is three times that of .the stator tooth. In his example, the frequency' attainable is the same as though the tooth pitch .of the two elements were the same, since the rotating element must be .displaced by a peripheral distance equal to the rotor pitch Pr in order to eii'ect a complete cycle of changes in magnetic .conductance. The important advantage .of this arrangement, therefore, lies in the increased width of slots for the wound element (either rotor or stator) which permits of substantial increased cross-section of active conductor metal and insulationv therefor as well as .of reduction of iro-n losses and heating. Compared with the construction of Fig. 1, it gives an increase of in conductor space, which permits of the generation of alternating current of increased amperage and voltage values, and as compared with the usual type of alternator `where ythe tooth pitches of rotor f and stator are equal, the present construction aiiords one and a half the total space for the winding and insulation of the active conductors. A general expression for the relationship of tooth pitches for Figs. 3 and 4 is stator pitel 2aXrotor pitch or P,=n P,. where n may be any whole number greater thanunity, `e. g. 2, 3, 4, etc. To demonstrate `by concrete example, the comparison between the construction of Figs. 3 and 4 with the usual arrangement of having the tooth pitch of the stator equal to that of the rotor, let us assume that the tooth pitch of the rotor in both cases be 4 1n. m. Where the tooth pitches are equal this gives a width of slot of only 2 m. m.; whereas 4in my improved construction the stator slot would be three times as large, i. e. 6 m. m., which aiiords ample space for the active conductors and their insulation.

Fig. 5 is illustrative of another permissible selected relationship between the pitch of rotor and stator teeth, and also between width of slots ot the two elements. The pitch of the teeth is in this case the same, while the stator slots are three times the width of those of the rotor, or three-fourths of the pitch of the teeth.

Fig. 5a shows a similar arrangement as regards relative tooth pitch, but here the slots Y of the rotor and stator elements are of equal width, each being three-fourths of the tooth pitch. With regard to Figs. 5 and l5, the general rule applicable in each lcase may be expressed as follows; `Assuming the same pitch for stator and rotor teeth e. PT.=P the stator slots ES may be 2nd-1 times th? width of a stator tooth, while the width of the rotor slot bears the same relation to the rotor tooth; or the width of a rotor tooth may be 21a-t1 times the width of the rotor slot,

where n is any whole number other `than Zero y(1, 2 and ,3, etes) The M. F. generated or induced in the windings ,of the Imachine ot Fig. 5 is roughly approximated by the curve ot Fig. 6,; and that generated by the modified arrangement ,of Fig. 5a would be similar as regards fre- .quency (for the same speed of rotation), but the loops of the curve would probably be somewhat ,di-Herent in shape due to the increase inwidth of the rotor slots.

It is 4obvious that Vthe principles and constructions so tar considered, are peculiarly applicable to va machine oi' the general type disclosed in vmy Patent No. 1,426,001; and to illustrate such application, let it be assumed that the construction of Fig. 5 or 5, is to be so applied. I-Iere the tooth pitches are equal, while the width of the stator slots is in general shown by the expression width of ZES-.1211+ 1 the width of a stator tooth or Ds, while the width of a rotor tooth is shown by the `equation width of DT=Qfa+l Width of a rotor slot Er, n being any whole number other than zero. t

The construction illustrated in Figs. 7, 7a and 8 is what may be termed a special caseor application of the principle ,disclosed in connection with Figs. 1 and 2. In the latter figures the expression of relationship was given as PVS 2n;- 1 where n may be any whole number. In the present modification a is selected as equal to ,Zero vso that the relationship oil pitches becomes XPf i. e. the pitch of the stator teeth is one-half `that of the'rotor teeth. In this example a has been selected equalto Zero but any whole number n will suit the purpose so that in this Acase also the general relationship of pitches becomes the same vas that given for Figs. 1 and 2 above. This is clearly illustrated in Figs, Iand .1, where the vrespective elements ,of the machine are indicated by the same reierence .characters as in the previously described tigures. The width of the stator slots ris three times that of a Istator tooth in Fig, Y?, and four times in Fig. 7. In general it may be m times as` great where m is any whole number equal to or greater than 2. In Fig.

8, the present invention is illustrated in Connection with a special form of machine, the particular characteristics of which are described in my prior patent above referred to, being shown in the drawings of said patent on Figs. 10-18 inclusive. This machine is characterized by ythe elliptical shape of the stationary element and further by the tact that the excitation or magnetizing winding is concentrated in a relatively small number of slots alternating current windings being lodged in a great number of regularly distributed peripheral slots. This winding O, O is shown by way of example, as concentrated in two slots M, M, although it may be less concentrated and be distributed around the wound element in a greater number of slots than those shown. The alternating current windings must, however, be so placed in slots ES as to insure the alternation of magnetic poles on the teeth Ds of the wound element.

Fig. 6l is an approximation of the E. M. F. curve produced in the alternator of Fig. 7, where the litactor m has been chosen equal to 4.

lf for m an uneven number be selected, the machine combining several such alternators should be composed of m identical parts the rotor or the stator of each part being displaced relatively to the adjacent part of the corresponding element by a peripheral displacement equal to pitch of the rotor teeth P divided by fm or Fig. 7 is illustrative of an elemental machine with m of the value oi' an uneven number 0r 3; and the E. M. F. generated in a machine combining several of these elements would increase the frequency in the ratio of mzl. The combined machine will therefore in each case, whether m is chosen an even or uneven number be composed ot' some uneven number of identical rotor and stator parts, one of each set of parts being displaced relatively to the corresponding adjacent part by a peripheral distance equal to an odd fraction of the pitch of the rotor teeth (Pr).

As has previously been indicated, it will be apparent to one skilled in this art, that in machines such as are herein considered, the rotor element may be the wound element and where such an arrangement is desirable, the relationship of tooth pitches, and relative width of slot described in the various figures for the stator element are applicable to the rotor element, the stator element in this case having the tooth pitch and slots which the unwound rotor had.

he windings O, 1 and 2 are so located within the stator slots, and the magnetic circuits are so arranged as to produce multiplication of the frequency of the working alternating current according to my Patent No. 1,426,001. The utility of such an arrangement consists in the possibility of multiplying the fundamental 'requency generated by the machine and also the possibility of use as a frequency changer for changing or multiplying the frequency of a current generated by a separate machine. The manner of accomplishing these results will be obvious by reference to the disclosure of said patent.

will be apparent that the arrangement of the stator or rotor teeth may be somewhat modilied Jfrom the specific construction illustrated without departing from the scope of the invention; for example, as shown in Fig. 9, the stator teeth may be arranged at an angle to the diametrical planes passing through the teeth. Among other advantages, this construction is found to enhance the cooling effect oi" the air currents produced by the movement of the rotor. Other modifications will doubtless occur to those skilled in the art which come within the scope of the invention as delined in the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. A dynamo-electric machine comprising rotor and stator elements each provided with tooth projections and intervening slots, and a magnetizing winding on one of said elements forming poles around its periphery, the magnetic circuits of which are completed through the other element, the Widths and spacing of the tooth projections on the respective elements being suoli that the reluc`v tance of the magnetic circuits varies 'from maximum to minimum for a movement of the rotor a distance not greater than one-half of the tooth width of theunwound element.

2. A dynaii'io-electric machine comprising rotor and stator elements each provided with tooth proj ctions and intervening slots, and an exciting winding on one of said elements forming alternate poles around its periphery, the magnetic circuits of which are completed through the other element, the tooth widths on both elements being approximately the same, the tooth pitch on the wound element being one and one-lialf times the tooth pitch on the other element and the slot width on the uiiwouiid element being approximately equal to the tooth width whereby the reluctance of the magnetic circuits varies troni maximum to minimum, for a movement ot the rotor a distance approximately equal to onelialf of the tooth width of the uiiwound element.

3. A dyiiaino-electric machine comjlirising stator and rotor elements each provided with tooth projections and intervening slots, an exciting winding on one of said elements forming alternate poles around its periphery the magnetic circuits of which are completed through the other element, the widths and spacing of the tooth projections on the respective elements being such that the reluctance of the magnetic circuits varies Afrom maximum to minimum for a movement of the rotor a distance not greater than one-halt oi the tooth 'width ot the unwound element, and a secondary winding arranged in inductive relation with the first-mentioned winding.

^ 4. A dynamo-electric machine comprising stator and rotor elements each provided rith tooth projections and intervening slots, and a magnetizing winding on one oi said elements forming poles around its periphery, the niagnetic circuits of which are completed through the other element, the median planes of the teeth of the Wound element being inclined to the cliainetrical planes passing through the teeth and the Widths and spacing of the tooth projections on the respective elements being such that the reluctance of the magnetic crcuts varies from maximum to minimum for a movement of the rotor a distance not greater than one-half of the tooth Width of the un- Wound element.

In testimony whereof, I have signed my a name to this speciiication. Y

NIKOLAI OBOUKHOFF. 

